The hydrofluorocarbons (HFC) and in particular the hydrofluoroolefins such as 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) are compounds known for their properties as refrigerants and heat-transfer fluids, extinguishers, propellants, foaming agents, swelling agents, gaseous dielectrics, polymerization or monomer media, support fluids, abrasive agents, drying agents and fluids for energy production units. Unlike CFCs and HCFCs, which are potentially dangerous for the ozone layer, HFOs do not contain chlorine and therefore do not pose a problem for the ozone layer.
Several processes for producing 1234yf are known.
WO2007/079431 describes the preparation of 1234yf by a process comprising the fluorination steps of 1233xf to 1,1,1,2-tetrafluoro-2-chloropropane (HFC244bb), followed by a dehydrochlorination step. The product 1233xf is prepared by trifluorination of the corresponding chlorinated precursor (CCl2═CClCH2Cl).
WP2008/054781 describes a preparation of 1234yf by reaction of 2,3-dichloro-1,1,1-trifluoropropane (243db) in the presence of HF on a catalyst, in particular the catalyst consisting in Cr/Co 98/2. The products of the reaction comprise 1234yf and 2-chloro-3,3,3-trifluoro-1-propene (1233xf), the latter product forming the major proportion; the other products 1-chloro-3,3,3-trifluoro-1-propene (1233zd) as well as 245cb and 1234ze are also formed. A higher temperature promotes the production of the isomer 1233zd. The starting product 2,3-dichloro-1, 1,1-trifluoropropane (243db) is indicated, without further details, as being obtained by chlorination of the trifluoro-1-propene (TFP).
WO2008/040969 and WO2008/075017 describe a substantially similar preparation. It is indicated that the reaction proceeds by dehydrochlorination of 243db to 1233 (xf as well as zd), followed by a reaction involving the formation of 1,1,1,2-tetrafluoro-2-chloropropane and the subsequent formation by dehydrochlorination of the 2,3,3,3-tetrafluoro-1-propene sought. The HF/organics ratio is varied and it is indicated that the dehydrochlorination reaction to 1233 (xf and zd) is promoted by low HF/organics ratios while the reaction of preparation of the final compound sought is promoted by high HF/organics ratios.
The starting product 2,3-dichloro-1,1,1-trifluoro-propane (243db) is indicated as being obtained by chlorination, without further details. of trifluoropropene or trifluoromethylpropene,
In these documents, no detail is given with respct of the preparation of the starting product, 243db. Although the chlorination reactions, in particular olefin chlorination, are known, there is no accurate description in the state of the art of a chlorination step of TFP to 243db.
WO 2005108334 describes the addition of a compound X1X2 to trifluoropropene, with X1 and X2 which can be independently chlorine. The addition of Cl2 to TFP is also indicated, as the first step before a fluorination reaction. However, the only examples relating to TFP are carried out with bromine and iodine, and furthermore in the presence of HF; in this document the 2,3-dibrominated or 2,3-diiodinated compound is neither isolated nor prepared.
The effective chlorination reaction of TFP to 243db is therefore not described in full in the technical literature.
There is a need for a process for the preparation of 1234yf from a starting product which is easily accessible, and which results in the obtaining of the sought product showing a high selectivity and advantageously a high yield and/or conversion.
There is also a need for a process for the preparation of 243db, a useful precursor in the preparation of 1234yf from a starting product which is easily accessible, and which results in the sought product showing a high selectivity and advantageously a high yield and/or conversion.